tekmar 274 Boiler Control User Manual

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Mode 3 - DHW in Primary/Secondary with No Priority
When a valid DHW Demand is present, the DHW relay
(terminal 17) and Primary Pump relay (terminal 18) turn
on. Heating zones are unaffected by DHW operation. This
mode can be used if the DHW tank is piped in parallel and
a DHW valve is installed (need to use an external relay to
power the valve with 24 V (ac) since the DHW pump output
is a 120 V (ac) powered output).

Mode = 3

DHW

Pump

Primary

Pump

Mode 4 - DHW in Primary/Secondary with Priority
When a valid DHW Demand is present, the DHW relay
(terminal 17) and Primary Pump relay (terminal 18) turn
on. If the boilers are unable to maintain the boiler target
temperature, space heating zones are shut off sequentially
using tN4 communication in order to provide priority to the
DHW tank.

Mode = 4

OFF

DHW

Pump

Primary

Pump

Mode 5 - DHW in Parallel / Last Boiler with Priority

When a valid DHW Demand is present, the DHW relay
(terminal 17) turns on and boiler pump 4 turns off. The control
uses the DHW Exchange Supply Sensor in order to measure
the boiler supply temperature supplied to the indirect tank.
There are two boiler target temperatures, one for the heating
system (BOIL TARGET) and one for the indirect DHW system
(BOIL DHW TARGET). In this mode, the DHW Demand can
only be provided from an External Powered Demand or tN4
Setpoint Control in DHW mode.

All boilers are used for space heating requirements
Boiler 2 is used for DHW when there is a DHW demand
The dedicated DHW boiler is always boiler 2 (relay 3),
even if there are less than 4 boilers.
If boiler 2 is disabled and mode 5 is selected then the
dedicated DHW boiler (boiler 2) will not operate.
This DHW mode is only available when control is in
Mode = 2

Mode = 5

OFF

DHW Pump

Primary

Pump

Boiler

Supply

Sensor

DHW Exchange

Supply Sensor

Mode 6 – Dedicated DHW
When a valid DHW Demand is present from the DHW
Sensor, the primary pump relay turns on. The DHW Relay
in this mode is used as the DHW recirculation pump and
operates continuously in the Occupied period and cycles
with the primary pump in the UnOccupied period. The boiler
plant is sequenced based only on the DHW Sensor.

All boilers are used for DHW requirements
Requires DHW demand from DHW sensor
DHW Pump Relay is used for DHW recirculation pump
Boiler Supply Sensor Not Required

Recirculation

Pump

DHW Sensor

On/

Off

On/

Off

Mode = 6

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